Use this weight loss calculator to help you reach your goal weight within a realistic time frame and maintain it. Calculations are based on a body model developed by the National Institute of Health.
Enter the time frame in which you would like to reach your goal weight and the calculator will tell you how many calories to intake daily to reach it. You can also specify an energy intake that’s workable for you and it will calculate the projected time frame to reach your goal weight.
The results of the calculations will show your projected weight loss or gain in tabular and graphical formats.
Enter your body parameters and your goal weight. If you don’t know your activity level, click the Estimate button for an estimation.
Select the Energy option and enter a start date and end date if your want to calculate the average daily energy intake you would need to reach your goal weight within that time frame.
Select the Time option and enter a start date and your planned daily energy intake to calculate an estimation of when your goal weight will be reached with that dietary intake.
Click Calculate and the results will be presented in tabular and graphic formats. Consult a doctor for guidance and support if you are considering a diet of less than 1,000 Calories (4,200 kilojoules) per day. Food group targets and nutrient recommendations will not be met below that level.
What is the science behind weight loss?
A change in body weight results from the difference between your food energy intake and the amount of energy expended by your body. Energy is burned in maintaining your body functions and in performing physical activities. For successful weight loss to occur, there must be an energy imbalance such that your energy expenditure is greater than your energy intake.
When you lose weight, where does the fat go?
When your body burns fat, 84 percent of it turns into carbon dioxide and is exhaled by your lungs. The remaining 16 percent becomes water and is expelled mostly by sweat and urine.
What causes water weight loss when dieting?
Your water weight loss is the weight of water released from glycogen. Low levels of glucose in the blood from dieting can trigger the release of needed glucose contained in glycogen molecules stored in your body. Each gram of glycogen is bound to 3 or 4 grams of water. As the glycogen stores deplete during the first few days of dieting, that water is released and excreted in the urine.
About the Calculations
This calculator uses formulas developed by Kevin Hall, Ph. D., and a team of researchers at the National Institute of Health. They are much more accurate in determining energy expenditure and energy requirements for the purpose of weight management. They challenge the popular 3,500 calories per pound rule by taking into consideration the physiological changes that take place during weight loss. This includes changes in body fat, muscle mass, the thermic effects of feeding, glycogen levels and sodium intake.
Along with your sex, age and basic body measurements, the formulas requires your body fat percentage value. The calculator roughly estimates it through an equation derived from research by Jackson et al on estimating percentage body fat from body mass index.
Your resting metabolic rate (RMR) or resting energy expenditure (REE) value is also required. The terms RMR and REE are generally used interchangeably and is a measurement of the energy burned by your body to keep it functioning while at rest. Both RMR and REE are usually measured by means of indirect calorimetry gas analysis. Such measurements can be taken at health clubs and some medical clinics but can be expensive and inconvenient. This calculator roughly estimates the value for you through a predictive Mifflin-St Jeor formula based on your height, weight, age and sex.
- Quantification of the effect of energy imbalance on bodyweight.
Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA.
Lancet (2011 Aug 27) 27;378(9793):826-37.
- The effect of sex, age and race on estimating percentage body fat from body mass index.
Jackson et al
International Journal of Obesity (2002) 26, 789–796
- A new predictive equation for resting energy expenditure in healthy individuals.
M D Mifflin, S T St Jeor, L A Hill, B J Scott, S A Daugherty, Y O Koh
The American Journal of Clinical Nutrition, Volume 51, Issue 2, February 1990, Pages 241–247